456 



THE MUSCULATURE 



between its origins from the vertebral bodies and discs and those from the transverse processes. 

 The nerves springing from the lumbar plexus take courses subject to much individual variation 

 through the muscle on the waj^ to their destinations. Fasciculi of the muscle may thus be 

 separated by the femoral (anterior crural) nerve or other branches of the lumbar plexus. 



The iliacus muscle in the region of the pelvis is covered by retro-peritoneal fat. The psoas 

 muscle crosses its medial margin and from between the two muscles the femoral nerve usually 

 emerges to pass into the thigh above the iliacus. Beyond the inguinal ligament the iliacus lies 

 in front of the capsule of the hip-joint and the straight tendon of the rectus femoris, and is 

 crossed by the sartorius. 



Fig. 406. — Psoas, Iliacus, and Quadratus Lumborum. 



Quadratus lumborum 



Psoas minor 



Psoas major' 



Iliacus 



Intertransversalis 

 anterior 



Quadratus lumborum 



Action. — The ilio-psoas is a powerful flexor of the thigh at the hip and a weak medial 

 rotator and adductor. It also serves to flex the lumbar region of the spine. 



Variations. — The j)S()as muscle may be separated from the iliacus as far as the femoral 

 insertion. The part of the psoas arising from the distal lumbar vertebra; may form a distinct 

 muscle. Slips may pass from the psoas major to the psoas minor. A separate lamina of the 

 iliacus muscle may be attached to the iliac fascia. From the anterior inferior iliac spine a small 

 muscle slip may run to the intertrochanteric line or the ilio-femoral ligament. To this slip the 

 term iliacus minor has been applied as well as to the larger fasciculus mentioned above. 



The psoas minor (fig. 406). — Origin. — From the twelfth thoracic and first lumbar vertebrse 

 and the intervening disc. 



Structure and insertion. — The fibre-bundles pass to be attached as far as the level of the fifth 

 lumbar vertebra to a flat tendon which appears about the mid-lumbar region and is inserted 

 into the ilio-pectincal eminence. It is intimately united to the iliac fascia. 



Nerve-supply. — The branch to the psoas minor arises usually from the first and second lum- 

 bar nerves, often in comi)ariy with the genito-femoral (genito-crural). 



Action. — To flex the pelvis. 



Relations. — It is closely applied to the ventral surface of the psoas major. 



Variations. — The muscle is inconstant in development and is frequently absent. Gruber 

 has found it absent on both sides in 183 out of 450 bodies, on one side in 69. 



BURS.(E 



B. iliopectinea. — A large bursa between the ilio-psoas muscle, the ilio-pectineal eminence, 

 and the capsule of the hip-joint. B. iliaca subtendinea. — A small bursa between the tendon 

 of insertion of the ilio-psoas and the lesser trochanter. 



